DESCRIPTION: (Applicant's Abstract) The long-term objective is to determine non-invasively the dynamics of neuronal populations involved in cortico-hippocampal signal processing during memory and learning in the human brain. The specific aim of this proposal is to evaluate the effects of different stimulus features and reactive output on current flow generated by coherent activation of neuronal populations in cortex, hippocampus and thalamus. The goal is to develop a method for the characterization of hippocampal function appropriate for both normal and patient populations. Potential clinical applications include the study of pathological conditions involving hippocampus: temporal lobe epilepsy, schizophrenia and learning and memory disorders. The method for achieving this goal is to measure the magnetic field simultaneously over the surface of the scalp with an array of 122 extremely sensitive magnetoencephalographic (MEG) sensors. The temporal resolution of MEG is excellent: sequential activation of multiple sources of current flow in the brain can be recorded on a millisecond time scale. Waveforms describing the temporal behavior and spectra reflecting the oscillatory behavior of current sources in thalamic, medial-temporal and cortical areas will be computed from the data utilizing a novel signal-space analysis algorithm. Evoked response and spectral-temporal measures of oscillatory activity will be determined for each source. Anatomical information about brain structures obtained from MRI scans for each subject will be utilized both in the analysis and for the display of neuronal population activity in specific cortical and subcortical areas. Electroencephalographic (EEG) recordings consistent with those used in clinical practice will be performed simultaneously with the MEG recordings for comparison with previous results. Subjects receive visual, auditory and somatosensory stimulation passively or with an imperative to respond with a simple motor output. Tasks involve orienting to novel stimuli, maintaining attention, remembering specific patterns of previously presented stimuli, learning associations between stimuli. Standard neurological tests for hippocampal function will be used: Sternberg paradigm with delayed memory testing: the unrelated word-pairs in the Wechsler Memory Scale. Auditory, visual and somatosensory oddballs will be used as probes. These stimuli are particularly appropriate for patient populations. Normal adults and school-age children of both sexes will be studied in groups of 10-15 subjects. Results will be presented both as individual responses and, when appropriate, as grand averages.